Difference between revisions of "Expressions"

Revision as of 13:27, 6 June 2007

FTM expressions are used in the following contexts

• the FTM message box (ftm.mess)
• FTM definitions (ftm.object)
• the expr class/object

The syntax is basically always the same appart from minor context dependent details.

Values and Lists

The values of FTM expressions can be int, float, symbol or references to FTM object. They values can be represended by the following terms:

• a simple value (int, float, symbol) such as '1', '2.3' and 'three'
• a named value such as $myobj
• an element of an object such as '$myobj[7]'
• a numberd argument such as '$1'

Examples of simple values are:

• 1 ... an int
• -2 ... an int
• 2.3 ... a float
• -4. ... a loat
• 5.67e-4 ... a float
• .89 ... a float
• ten ... a symbol
• 11-12 ... a symbol (because no space!)
• -thirteen ... a symbol

Named values are defined by FTM definitions using ftm.object. The names, always representing a single value, are used in expressions with a leading dollar – '$' – making for example:

• $x
• $myobject

An element of an object can be accessed with FTM expressions using brackets – '[' and ']', for example:

• $myvec[0]
• $mymat[0 0]
• $mydict[x]

Anything more complex than $-names and []-elements has to happen within parenthesis (see below).

Single values can be concatenated to argument lists (in the message box lists or messages) with spaces like:

• 1 2.3 three
• 4 + 5.5 / six (this is a list of 5 elements)
• $myobj set 7 9.8 ten

Argument lists within parenthesis will be evaluated (see below).

Parenthesis

Parenthesis in FTM expressions – '(' and ')' – always will (try to) evaluate the contained elements to a single value.

Inside parenthesis you'd have either one

• a value such as '(1)' or '($x)' or '($mydict[x])' (in which case the parenthesis are useless)
• an infix expression such as '(4 + 5.5 / $six)'
• a prefix expression such '(random -90 0)' or '($myobj set 7 9.8 ten)'